FIELD-EFFECT PASSIVATION OF HIGH-EFFICIENCY SILICON SOLAR-CELLS

In this paper effective surface recombination velocities S(eff) at the rear Si-SiO2 interface of the presently best one-sun silicon solar cell structure are calculated on the basis of measured oxide parameters. A new cell design is proposed allowing for a control of the surface space charge region by a gate voltage. It is shown that the electric field introduced by the positive fixed oxide charge density typically found at thermally oxidized silicon surfaces and the favorable work function difference between the gate metal aluminum and silicon leads to a reduction of S(eff) to values well below 1 cm/s at AM1.5 illumination for n-type as well as p-type silicon. At low illumination levels, however, oxidized n-type silicon has much better surface passivation properties than p-type silicon due to the small hole capture cross section (sigma(n)/sigma(p) almost-equal-to 1000 at midgap). Only at small illumination intensities for p-type substrates or in the case of poor Si-SiO2 interface quality the incorporation of a gate electrode on the rear surface is a promising tool for further reducing surface recombination losses.